The book of Exodus in the Tanach (Hebrew Bible, Old Testament) characterizes God by thirteen attributes: "The Lord, the Lord, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness, keeping steadfast love for thousands, forgiving iniquity and transgression and sin, but who will by no means clear the guilty, visiting the iniquity of the fathers upon the children and the children's children, to the third and the fourth generation."

The Tanach (Hebrew Bible, Old Testament) contains no systematic theology: No attempt is made to give a philosophical or rigorous definition of God, nor of how God acts in the world. The Tanach does not explicitly describe God's nature, exemplified by God's assertion in Exodus that "you cannot see my face; for man shall not see me and live." The Tanach does, however, provide a poetic depiction of God and His relationship with people. According to the biblical historian Yehezkal Kaufmann, the essential innovation of Biblical theology was to posit a God that cares about people, and that cares about whether people care about Him. Most people believe that the Bible should be viewed as humanity's view of God, but theologian Abraham Joshua Heschel described the Biblical God as "anthropopathic," and said that we should read the Bible as God's view of humanity.

Similarly, the New Testament also contains no systematic theology: No attempt is made to give a philosophical or rigorous definition of God, nor of how God acts in the world. The New Testament does, however, provide an implicit theology as it teaches that God became human while remaining fully God, in the person of Jesus Christ. In this view, God is something that can be seen and touched, and may speak and act in a manner easily perceived by humans. This is a radical departure from the concepts of God found in the Hebrew Bible and in the Quran. The New Testament's statements regarding the nature of God were eventually developed into the doctrine of the Trinity.

In his book on first philosophy, which most now call the Metaphysics, Aristotle discussed the meaning of "being as being". Some see contradictions in this book, and conclude that it puts together many different works that Aristotle wrote at different times. Others find a coherent argument in the book. According to the latter reading, Aristotle concluded that "being" primarily refers to the Unmoved Movers, and assigned one of these to each movement in the heavens. In the Aristotelian theory each Unmoved Mover continuously contemplates its own contemplation, and everything that fits the second meaning of "being" by having its source of motion in itself, moves because the knowledge of its Mover causes it to emulate this Mover (or should). This influenced Anselm's view of God, who he called "that than which no greater being can be conceived". Anselm thought that God did not feel emotion such as anger or love, but appeared to do so through our imperfect understanding. The incongruity of judging "being" against something that might not exist may have led Anselm to think that he had proved God's existence.

Many medieval philosophers developed the idea of approaching a knowledge of God through negative attributes. For example, we should not say that God exists in the usual sense of the term; all we can safely say is that God is not nonexistent. We should not say that God is wise, but we can say that God is not ignorant, i.e. in some way God has some properties of knowledge. We should not say that God is One, but we can state that there is no multiplicity in God's being.

Aristotle devotes special attention to the Platonic theory, according to which ideas are the ultimate principles of Being. That theory, he contends was introduced to explain how things are, and how things are known; in both respects, it is inadequate. To postulate the existence of ideas apart from things is merely to complicate the problem; for, unless the ideas have some definite contact with things, they cannot explain how things came to be, or how they came to be known by us. Plato does not maintain in a definite, scientific way a contact between ideas and phenomena -- he merely takes refuge in expressions, such as participation, imitation, which, if they are anything more than empty metaphors, imply a contradiction. In a word, Aristotle believes that Plato, by constituting ideas in a world separate from the world of phenomena, precluded the possibility of solving by means of ideas the problem of the ultimate nature of reality.

What, then, are, according to Aristotle, the principles of Being? In the metaphysical order, the highest determinations of Being are Actuality (entelecheia) and Potentiality (dynamis). The former is perfection, realization, fullness of Being; the latter imperfection, incompleteness, perfectibility. The former is the determining, the latter the determinable principle. Actuality and potentiality are above all the Categories; they are found in all beings, with the exception of the Supreme Cause, in Whom there is no imperfection, and, therefore, no potentiality. God is all actuality, Actus Purus. All other beings are composed of actuality and potentiality, a dualism which is a general metaphysical formula for the dualism of matter and form, body and soul, substance and accident, the soul and its faculties, passive and active intellect. In the physical order, potentiality and actuality become Matter and Form. To these are to be added the Agent (Efficient Cause) and the End (Final Cause); but as the efficiency and finality are to be reduced, in ultimate analysis, to Form, we have in the physical order two ultimate principles of Being, namely, Matter and Form. The four generic causes -- Material, Formal, Efficient, and Final -- are seen in the case, for instance, of a statue:

The Material Cause[?], that out of which the statue is made, is the marble or bronze.

The Formal Cause[?], that according to which the statue is made, is the idea existing in the first place as exemplar in the mind of the sculptor, and in the second place as intrinsic, determining cause, embodied in the matter.

The Final Cause[?] is that for the sake of which (as, for instance, the price paid the sculptor, the desire to please a patron, etc.) the statue is made.

Mere potentiality without any actuality or realization--what is called materia prima--nowhere exists by itself, though it enters into the composition of all things except the Supreme Cause. It is at one pole of reality, He is at the other. Both are real. Materia prima possesses what may be called the most attenuated reality, since it is pure indeterminateness, God possesses the highest and most complete reality, since He is in the highest grade of determinateness. To prove that there is a Supreme Cause is one of the tasks of metaphysics the Theologic Science. And this Aristotle undertakes to do in several portions of his work on First Philosophy. In the "Physics" he adopts and improves on Socrates' teleological argument, the major premise of which is, "Whatever exists for a useful purpose must be the work of an intelligence". In the same treatise, he argues that, although motion is eternal, there cannot be an infinite series of movers and of things moved, that, therefore, there must be one, the first in the series, which is unmoved, to proton kinoun akineton--primum movens immobile.

In the "Metaphysics" he takes the stand that the actual is of its nature antecedent to the potential, that consequently, before all matter, and all composition of matter and form, of potentiality and actuality, there must have existed a Being Who is pure actuality, and Whose life is self-contemplative thought (noesis noeseos). The Supreme Being imparted movement to the universe by moving the First Heaven, the movement, however, emanated from the First Cause as desirable; in other words, the First Heaven, attracted by the desirability of the Supreme Being "as the soul is attracted by beauty", was set in motion, and imparted its motion to the lower spheres and thus, ultimately, to our terrestrial world. According to this theory God never leaves the eternal repose in which His blessedness consists. Will and intellect are incompatible with the eternal unchangeableness of His being. Since matter, motion, and time are eternal, the world is eternal. Yet, it is caused. The manner in which the world originated is not defined in Aristotle's philosophy. It seems hazardous to say that he taught the doctrine of Creation. This much, however, may safely be said: He lays down principles which, if carried to their logical conclusion, would lead to the doctrine that the world was made out of nothing or always existed.

Aristotelian theology was accepted by many later Jewish philosophers, such as Maimonides, Gersonides, Samuel Ibn Tibbon and many others; their views of God are considered mainstream by many Jews of all denominations even today. Aristotelian theology was also accepted by many later Christian and Islamic philosophers and theologians in the medieval era.

Kabbalah (Jewish esoteric mysticism) teaches that God is neither matter nor spirit. Rather God is the creator of both, but is Himself neither. But if God is so different than His creation, now can there be any interaction between the Creator and the created? This question prompted Kabbalists to discuss two aspects of God, (a) God Himself, who in the end unknowable, and (b) the revealed aspect of God who created the universe, preserves the universe, and interacts with mankind. Kabbalists claim that these two aspects are not contradictory but complement one another.

Some Kabbalistic Jews, such as Moses Cordovero and Lubavitch (Chabad) Hasidism, claim that the first aspect of God is actually all that there really is. Nothing exists except for God, and all else is an illusion. (Depending on how this is explained, such a view can be considered panentheism, or pantheism.) Most other Kabbalists hold that there is an aspect of God that is reavealed to the world.

Kabbalists speak of the first (a) aspect of God as "En Sof"; this is translated as "the infinite," or "that which has no limits". They teach that nothing can be said about this aspect of God. This aspect of God is impersonal, and not anthropomorphic at all. Kabbalists speak of the second (b) aspect of God as being seen by the universe as ten emanations from God; these emanations are called "sefirot."

The sefirot mediate the interaction of the ultimate unknowable God with the physical and spiritual world. Some explain the sefirot as stages of the creative process whereby God, from His own infinite being, created the progression of realms which culminated in our finite and physical universe. Others suggest the sefirot may be thought of as analogous to the fundamental laws of physics. Just as gravity, electro-magnetism, the strong nuclear force, and the weak nuclear force allow for interactions between matter and energy, the ten sefirot allow for interaction between God and the Universe.

The difficulty with this view is that the Kabbalah teaches that the Sefirot are not distinct from the Ein-Sof, but are somehow within it. The idea that there are ten divine sefirot could evolve over time into the idea that "God is One being, yet in that One being there are Ten". This would be almost the same as the Christian belief in the Trinity, which states that while God is "One", in that One there are Three persons. This new view Kabbalah in fact did occur among a small number of Jews in the 17th century. Rabbi Leon Modena, a 17th century Venetian critic of kabbalah, wrote that if we were to accept the Kabbalah, then the Christian trinity would indeed be compatible with Judaism, as the Trinity closely resembles the Kabbalistic doctrine of sefirot. This critique was in response to the fact that some Jews went so far as to address individual sefirot individually in some of their prayers. Kabbalah had many other opponents, notably Rabbi Yitzchak ben Sheshet Perfet (The Rivash); he stated that Kabbalah was "worse than Christianity", as it made God into 10, not just into three. The critique, however, was unfair. Most followers of Kabbalah never believed this. The Christian Trinity concept posits that there are three persons existing within the Godhead, one of whom literally became a human being. In contrast, the Kabbalistic sefirot have no mind or intelligence, they are not addressed in prayer, and they can not become a human being. They are conduits for interaction - not persons or beings.

Kabbalists seem to have identified the tenth sephira, Malkuth or the Kingdom, with Earth or the world of perception. Each sephira emanated from the number or numbers before it, so in a sense the first sephira, Kether or the Crown, created everything else. However, at least some of them attributed the creation of Kether to the limitless light, Ain Soph Aur. Some also called the light Ain, or the Nothing. Some Kabbalists used the names of the sephiroth and Ain to mean certain 'mental' states.

Today all Hasidic Orthodox Jews are Kabbalistic; some non-Hasidic Orthodox Jews are kabbalisticly inclined, while some are rationalists. Most Reform and Conservative Jews are rationalists.